Current lidar systems scan the environment to build a point cloud which in turn delivers a detailed understanding of the shape and location of the lidar's surroundings to any of a variety of scene understanding systems, such as vehicle navigation and autonomous vehicle (AV) systems. Advanced lidar systems may operate by scanning emitted light through a sequence of horizontal rows or scan lines. A receiver then records the return from each emitted pulse or wave along each scan line. After traversing all of the rows, and capturing all of the returns, a single frame has been captured by the lidar imager. The frame rate, i.e. the rate at which single frames are captured, is affected by the number of points on each row and the number of rows that are scanned to capture a full frame.
As the distance and detail detected by a lidar system increases, the speed of the system and, in particular, the frame rate decreases. The scan rate can be limited by such factors as the light pulse's travel time from the lidar to an object and back, the time required to scan the emitted beam, and the number and width of rows to be scanned. These factors all drive the system toward a lower frame rate. In other words, as the size and resolution of the lidar frame increases, the time required for the lidar to scan all of the rows required to make a complete image also increases. A slower frame rate increases both latency in the system and increases global and local motion artifacts. Some of these factors can be overcome with additional computational power, faster mirror scanners and other measures. Some of the factors, such as longer travel time from the lidar to a more distant target cannot be overcome.
It is possible to drive the scanner of the lidar in a different mode so that only a small part of the full frame is captured. A smaller scan area allows a higher frame rate, higher resolution, or faster result to be captured for the small area than for a full scan. By interrupting the normal full frame scan for a detail scan, the lidar obtains detailed information about a partial area of the scene at the cost of delaying the next full frame scan.
To interrupt a normal full frame scan, a small area must be selected. For an AV, most of the vehicle surroundings do not usually include details that are important for navigation. In some systems, a visual light camera is used in AV systems to compensate for the slower frame rate of the lidar. The camera images are processed to select areas of interest. The lidar can be directed to perform a more detailed scan of the selected areas.